Transcript L2-H2 receptors and proton pump inhibitor2014-11

Drugs in peptic ulcer
(H2 blockers and proton pump inhibitors)
By
Prof. Hanan Hagar
Peptic ulcer
a localized lesion of the mucous membrane of the
stomach (gastric ulcer) or duodenum (duodenal
ulcer), typically extending through the muscularis
mucosa.
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Pathophysiology:
is imbalance between aggressive factors (acid &
pepsin) and defensive factors (e.g. prostaglandins,
mucus & bicarbonate layer). However, nowadays, it
seems that H. pylori theory is very important.
Helicobacter pylori is the major etiological factor
in peptic ulcer disease (PUD).
Etiology:
H.
pylori infection
Alcohol
Smoking
Caffeine
Genetic factors
Diet
Hypersecretory states (Zollinger Ellison syndrome)
Drugs (e.g.) NSAIDs
Gastric secretions
1.
2.
3.
HCl and intrinsic factor (Parietal cells).
Pepsinogens (Chief cells).
Mucus, bicarbonate (mucus-secreting cells).
Regulation of gastric secretions
Parietal cells secrete acid in response to:
1.
2.
3.
4.
Histamine (local hormone): H2 receptors
Gastrin (hormone): CCK2 receptors
Ach (neurotransmitter): M3 receptors
Proton pump (H+/ K+ ATPase)
Treatment of peptic ulcer
Eradication of H. pylori infections
Hyposecretory drugs.
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Mucosal cytoprotective agents.
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Proton pump inhibitors
H2 receptor blockers
Antimuscarinic drugs
Prostaglandin analogues
Neutralizing agents (antacids).
Gastric hyposecretory drugs
Include:
 Proton pump inhibitors
 H2 receptor blockers
 Antimuscarinic drugs
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Hyposecretory drugs decrease gastric acid
secretion Promote healing & relieve pain.
Proton Pump Inhibitors (PPIs)
Omeprazole – Lansoprazole
Pantoprazole -Raprazole
Acts by irreversible inhibition of proton pump
(H+/ K+ ATPase) that is responsible for final step
in gastric acid secretion from the parietal cell.
Gastric secretion by parietal cells
Pharmacodynamics of PPIs
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They are the most potent inhibitors of acid
secretion available today.
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Produce marked inhibition of basal & meal
stimulated-acid secretion (90-98%).
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Reduce pepsin activity.
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Promote mucosal healing & decrease pain
Pharmacokinetics of PPIs
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Given orally as enteric coated capsules
(unstable in acidic medium in stomach).
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Are pro-drugs
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rapidly absorbed from the intestine.
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In the acidic medium of parietal cell
canaliculi, they are activated.
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Should not combined with H2 blockers or
antacids.
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At neutral pH, PPIs are inactivated.
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Have long duration of action (> 12 h-24 h).
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Once daily dose is sufficient
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Given 1 h before meal.
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Bioavailability is reduced by food.
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metabolized in the liver by Cyt-P450.
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Dose reduction is required in severe liver
failure.
USES of PPIs
Eradication
of H. pylori (combined with
antimicrobial drugs).
Resistant

severe peptic ulcer ( 4-8 weeks).
Reflux esophagitis.
Hypersecretory
conditions as Zollinger Ellison
syndrome and gastrinoma (First choice).
Zollinger Ellison syndrome
Gastrin -secreting tumor of the pancreas.
Gastrin produces:
 Parietal cell hyperplasia (trophic factor).
 Excessive gastric acid production.
Adverse effects to PPIs
Headache, diarrhea & abdominal pain.
 Achlorhydria
 Hypergastrinaemia.
 Gastric mucosal hyperplasia.
- Increased bacterial flora
- increased risk of community-acquired respiratory
infections & nosocomial pneumonia
 Long term use:
 Vitamin B12 deficiency
 increased risk of hip fractures
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H2 receptor blockers
- Cimetidine - Ranitidine
- Famotidine - Nizatidine
Mechanism of action
 They competitively and reversibly block
H2 receptors on the parietal cells.
Pharmacokinetics
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Good oral absorption
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Given before meals.
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Famotidine is the most potent drug.
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Exposed to first pass metabolism (except
nizatidine that has 100 % bioavailability).
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Duration of action (4-12 h).
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Metabolized by liver.
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Excreted mainly in urine.
Pharmacological actions:
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Reduce basal and food stimulated-acid
secretion
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Block 90% of nocturnal acid secretion (which
depend largely on histamine) & 60-70% of total
24 hr acid secretion. Therefore, it is better to be
given before night sleep.
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Reduce pepsin activity.
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Promote mucosal healing & decrease pain
Uses:
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GERD ((heartburn/ dyspepsia).
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Acute ulcer healing in moderate cases
 Duodenal
 Benign
Ulcer (6-8 weeks).
gastric ulcer (8-12 weeks).
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Pre-anesthetic medication (to prevent
aspiration pneumonitis).
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Prevention of bleeding from stress-related
gastritis.
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Post–ulcer healing maintenance therapy.
Adverse effects of H2 blockers
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GIT disturbances (Nausea & Vomiting).
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CNS effects: Headache - confusion
(elderly, hepatic dysfunction, renal dysfunction).
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Bradycardia and hypotension (rapid I.V.)
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CYT-P450 inhibition (Only Cimetidine)
decrease metabolism of warfarin, phenytoin,
benzodiazepines.
Endocrine effects (Only Cimetidine)
 Galactorrhea (Hyperprolactinemia )
 Antiandrogenic actions (gynecomasteia –
impotence) due to inhibition of
dihydrotestosterone binding to androgen
receptors.
Precautions
Dose reduction of H2 RAs in severe renal or
hepatic failure and elderly.
Antacids
These drugs are mainly inorganic salts
e.g.: NaHCO3; Ca CO3; Al (OH)3; Mg (OH)2
 acts by direct chemical neutralization of HCL and as
a result may decrease pepsin activity.
 used to relief pain of peptic ulcer & for dyspepsia.
 All antacids  absorption of some drugs as
tetracycline, fluoroquinolones, iron.
NaHCO3: Systemic alkalosis
Ca CO3 : milk alkali syndrome (hypercalcemia, renal failure)
Al (OH)3 : constipation; Mg (OH)2 : Diarrhea
Misoprostol
 Prostaglandin analogues (PGE1 )
  HCL secretion.
  protective measures ( mucous/bicarbonate
& gastric mucosal blood flow).
 Orally, must be taken 3-4 times/day.
 Used for NSAIDS-induced peptic ulcer.
Adverse effects:
 Abdominal cramps; diarrhea
 Uterine contraction (dysmenorrhea
bleeding.
or abortion);vaginal
Summary
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Test for H. pylori prior to beginning therapy.
Acid-reducing medications for PUD include:
 H2RAs
 PPI’s should be used for acute therapy only if H2RAs
fail or cannot be used, or as part of treatment for H.
pylori.
Complete H. pylori eradication is required to prevent
relapse.
Maintenance therapy can be given until successful H.
pylori eradication.